I can think of a few things that can cause that kind of thing. Instrument movement, AI Traffic movement, Airport traffic (not the just the aircraft), plus other things.

Mine are most stable at high altitude, but they can get jumpy as you get near the ground (Extremely Dense scenery) or complex airport scenery. I ignore it when that happens. If you lower your Scenery Complexity slider it coud improve (mine is set to dense).


Just ignore that the Leve of detail is circled. I borrowed the image from my other reply.

My advise is to play with the settings until you are happy with what you have (with regards to frame rates versus scenery complexity). Have you done this http://www.venetubo.com/fsx.html fix yet?

Mark